Pickup cartridge with magnet armature having opposite axial sides of like polarity and central portion of opposite polarity

ABSTRACT

A small-sized light stylus pressure pickup cartridge with superior characteristics having an armature comprising a permanent magnet plate with both of its sides magnetized in opposite polarity from its central portion, a substantially inverted channel-shaped yoke or yokes arranged in the proximity of the outer sides of the magnet, a stylus arm fixed on the magnet and a reproducing stylus; characterized in that movement of the stylus is transmitted to the magnet thereby obtaining a corresponding electrical output from a coil or coils wound on a yoke or yokes.

Ilite States Patent Morita Oct. 2, 1973 PICKUP CARTRIDGE WITII MAGNET ARMATURE HAVING OPPOSITE AXIAL SIDES OF LIKE POLARITY AND'CENTRAL PORTION OF OPPOSITE POLARITY Katsuhiko Morita, Osaka, Japan Matsushita Electric Industrial Co., Ltd., Osaka, Japan Filed: Jan. 19, 1972 Appl. No.: 218,983

Inventor:

Assignee:

Foreign Application Priority Data Feb. 23, 1971 Japan 46/8791 [1.5. CI. 179/100.41 K, 179/100.41 M Int. Cl ..1104r11/12 Field of Search 179/100.41 M, 100.41 K,

References Cited UNITED STATES PATENTS 12 1971 Matsuda '179 10041 K 2,610,259 9/1952 Robertson 179/120 FOREIGN PATENTS OR APPLICATIONS 478,502 10/1969 Switzerland 179/1004] K Primary Examiner-Raymond F. Cardillo, Jr. Attorney Richard K. Stevens et al.

[57] ABSTRACT A small-sized light stylus pressure pickup cartridge with superior characteristics having an armature comprising a permanent magnet plate with both of its sides magnetized in opposite polarity from its central portion, a substantially inverted channel-shaped yoke or yokes arranged in the proximity of the outer sides of the mag net, a stylus arm fixed on the magnet and a reproducing stylus; characterized in that movement of the stylus is transmitted to the magnet thereby obtaining a corresponding electrical output from a coil or coils wound on a yoke or yokes.

13 Claims, 16 Drawing Figures PATENTEU 2 I973 SHEET 10F 5 PRIOR'ART FIG.

FIG. 2b

FIG. 20

PATENTED 2 73 sum 2 [IF 5 FIG. 4d

Till

PATENTED 2 I973 SHEET 3 BF 5 PICKUP CARTRIDGE WITH MAGNET ARMATURE HAVING OPPOSITE AXIAL SIDES OF LIKE POLARITY AND CENTRAL PORTION OF OPPOSITE POLARITY The present invention relates to a pickup cartridge used for reproduction from a stereophonic disc record.

The conventional pickup cartridge of the kind employing a columnar magnet as shown in FIG. 1 is widely used. This pickup cartridge comprises a stylus arm 2 with a reproducing stylus l fixed on its end, a columnar magnet 3 north (N) -south (S) polar magnetized in longitudinal direction of the stylus arm, a damper 4 for elastically supporting the central portion of the magnet 3 and a yoke 5. When the reproducing stylus l vibrates, magnetic fluxes occur in the yoke in response to the movement of the stylus 1, whereby an output voltage is produced in the coil 6 wound on the yoke 5. In this pickup cartridge, since the columnar magnet 3 acts as an armature, the moment of inertia is inevitably large due to its manner of arrangement. For this reason, the effective mass of the moving system which effects the fundamental characteristics of the pickup cartridge is considerably high. This not only imposes a limit on the ability to reproduce high frequencies but increases the mechanical impedance, which in turn restricts the degree to which the stylus pressure is reduced. This problem may be solved by reducing the size of the columnar magnet 3, but such a step is accompanied by the disadvantage of a lower output voltage.

Accordingly, it is an object of the present invention to provide a reproducing pickup cartridge for use with a stereophonic disc record, which operates on the principle of efficient voltage generation by perfect magnetic flux alternation and which is characterized by an armature composed of a plate magnet with large coercive force and with a small moment of inertia as well as by a yoke having a simple construction, thereby obtaining a high output, reproduction over a wide range of frequencies, a low mechanical impedance and a high signal to noise ratio.

The above and other objects, features and advantages will be made apparent by the detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram showing the construction of the essential parts of the conventional pickup cartridge;

FIG. 2a is a diagram showing the construction of the essential parts of the pickup cartridge embodying the present invention;

FIG. 2b shows the construction of the essential parts of the stereo pickup cartridge of the 45-45 type according to the invention;

FIGS. 3a, 3b and 3c are diagrams for explaining the operation of the device according to the invention;

FIGS. 40, 4b, 4c and 4d show front and side views of armatures embodying the present invention;

FIG. 5 is a diagram showing the construction of the essential parts of another embodiment of the present invention;

FIG. 6 is an exploded perspective view of the essentinl parts of the pickup cartridge showing an actual construction of the embodiment of FIG. 5;

FIG. 7a is a diagram showing the construction of the essential parts of a monoral pickup cartridge according to another embodiment of the present invention;

FIG. 7b shows a perspective view of the device of FIG. 7a; and

FIGS. 8a and 8b show respectively the construction and a perspective view of the essential parts of the stereo pickup cartridge of the 4545 type according to still another embodiment of th present invention.

An example of the construction of the pickup cartridge according to the present invention is shown in FIG. 2. In this figure, the pickup cartridge is so constructed that a magnetic axis is set up in the transverse direction of a flat magnet plate with a small length-todiameter ratio. The armature 7, comprising a permanent magnet which is magnetized in such a manner that north poles (or south poles) are set up on both sides and a south pole (or a north pole) is formed in the central portion thereof, is coupled with a stylus arm 26 with a reproducing stylus mounted on its end. A support member 11 with a notch portion 10 is arranged as an axial extension of the stylus arm so that the armature 7 moves with a central portion thereof as a supporting point. The yoke 15 which is made of an alloy with a high magnetic permeability has pole pieces 16 and 17 on its ends which are placed on either side of the armature 7 and in its proximity. A coil 18 is wound on the yoke 15.

The principle of operation of the above-described pickup cartridge will be now explained with reference to FIGS. 3a to 3c. In the event that the record disc 24 in FIG. 3a has un-modulated grooves, the armature 7 is placed at a neutral position between the pole pieces 16 and 17 as shown in FIG. 3a, in which case magnetic fluxes mainly flow from the north to south poles along paths as shown by arrow A, while little magnetic flux occurs in the yoke 15. This is probably due to a high magnetic resistance of the air gaps and the magnetic fluxes, if any, flow in opposite directions through the yoke to thereby cancel each other. On the other hand, when the reproducing stylus 25 is moved to a lower position due to modulated grooves of the record disc as shown in FIG. 3b, the pole end 8 of the armature 7 approaches the pole piece 16 of the yoke 15, while the other magnetic pole 9 of the armature 7 moves away from the pole piece 17 of the yoke 15. Under these conditions, magnetic fluxes flow in the yoke 15 in the direction of arrow B, thereby inducing an electromotive force e in the direction of arrow B in the coil 18. Also, in the case where the reproducing stylus 25 is moved upwards to a position as shown by FIG. 30 due to modulated grooves of the record disc 24, the magnetic pole 9 of the armature 7 moves close to the pole piece 17 and the other magnet pole 8 moves further away from the pole piece 16, As a result, magnetic fluxes flow in the opposite direction from the case of FIG. 3b, thereby inducing an electromotove force in the direction of arrow C. In this way, magnetic fluxes corresponding to the motion of the reproducing stylus 25 alternate in the yoke 15, so that an output voltage is produced in the coil 18 wound on the yoke 15. The armature 7 is magnetized in such a manner as is illustrated in FIG. 2a. This armature magnet consists of the two magnet plates 8 and 9 which are magnetized individually and bonded to each other with sides of the same polarity fixed to each other. Since self-demagnetization occurs in the armature 7, a barium ferrite magnet or a platinum-cobalt alloy magnet with a large coercive force is more suitably used as the armature than a cast magnet with a small corecive force. In order to obtain a high output voltage, it is desirable to employ a magnet with anistropic magnetic properties. To be specific, the barium ferrite magnet may be obtained in any desired shape by a pressing process. Also, its specific gravity is lower than that of a metallic magnet and less grinding processes are required, contributing to lower production cost. Other advantages of a barium ferrite magnet include a large coercive force and a magnetic permeability which is almost equal to air, thus permitting it to be magnetized in any desirable manner. The section of the armature 7 may take various forms including a simple circle as shown in FIG. 4, or a cross, V shape or semi-circle. This armature is provided with a center hole 12 for receiving the stylus arm 26. Also, the stylus arm 26 may be coupled with the armature in a different manner. Further, the armature 7 may be magnetized partially only at the shadowed portion 13 in the proximity to the pole pieces 16 and 17.

As mentioned above, the armature 7 consists of the two magnetized plates attached to each other with the sides of the same polarity inside, and therefore it is possible to increase the density of magnetic fluxes. In addition, since the armature 7 consists of a flat plate in shape, the moment of inertia can be greatly lessened, in comparison with the conventional device employing a bar magnet, by pivot-supporting the portion of the armature near its center of gravity. This leads to a smaller effective mass of the vibration system from the viewpoint of the reproducing stylus, thereby contributing greatly to the improvement in the performance of the pickup cartridge.

Also, in order to allow appropriate motion of the armature 7 in the neighborhood of the supporting point 14, it is recommended that a notch portion is made of elastic, strong and thin metal wire such as phosphorus bronze or plastic material so that the end portions of the armature 7 which are opposed to the pole pieces of the yoke vibrate in response faithfully to the motion of the reproducing stylus in a given direction. Moreover, a damper 23 made of elastic material such as butyl rubber is interposed between the armature 7 and the support 11 as shown in FIG. 6, whereby the space between the support 11 and the armature 7 is regulated to obtain an appropriate compliance and damping of the reproducing stylus.

A stereo pickup cartridge of the 4545 type embodying the present invention is shown in FIG. 2b. The yokes 15R and 15L shown in FIG. 2b which are fundamentally of an inverted channeLshape and made of an alloy with high magnetic permeability such as permalloy are disposed in proximity to each other in such a manner that the pole pieces 16R and 17R; 16L and 17L of the yokes 15R and 15L are repectively astride the disc armature 7 at an angle of 45 to the plane which contains the axis of the tip of the reproducing stylus and the main axis of the stylus arm 26 and which is at right angles to the surface of the record disc 24, said yokes being placed at right angles to each other in the planes R and L respectively containing the supporting point 14.

In this construction of the stereo pickup cartridge, the edges of the pole pieces 16R, 17R, 161.. and 17L come closest to the armature 7 when the pole pieces are in the above-mentioned local relationship with each other. In this case, however, other portions of the yokes than the edges thereof may be differently shaped. On the other hand, the pole pieces 16R, 17R, 16L and 17L are so shaped at their ends that the magnetic resistance in them is the least when they are set at 45 as mentioned above. Also, the armature 7 may be either interposed between the pole pieces 16 and 17 or the pole pieces 16 and 17 may be located within the levels of both side surfaces of the magnet 7.

In this case, the pickup cartridge operates as described below. Referring to FIG. 2b, when the reproducing stylus 25 changes its position in the direction of arrow D (leftward at 45), the coil 18L wound on the yoke 15L located to the right of the reproducing stylus 25 produces an output voltage on the same principle as in its relocation in vertical directions as described earlier. However, no output voltage is produced in the coil 18R wound on the left yoke 15R since the armature 7 moves only around the R axis. As a result, signals of the two channels are separated. When the reproducing stylus is relocated rightward at 45, by contrast, an output voltage is produced in coil 18R, while no voltage is generated in coil 18L. With the vibration of the reproducing stylus in other ways, output voltages proportionate to the vector components in the direction of the pole pieces are generated in the coils, thereby making it possible to reproduce stereo sound from the stereo rec'ord disc.

Another embodiment of the invention is illustrated in FIG. 5. In this cartridge, the coils 18 are wound on both legs of the yoke 15 and are connected in series so that output voltages thereof are combined with each other. This arrangement permits the output voltage e to be twice as high as the preceding embodiment, whereby it is possible to dampen the noise voltages due to externally leaked noise magnetic fluxes generated in the motor and transformer, thus improving the signal to noise ratio remarkably.

FIG. 6 shows an actual example of the construction of the stereophonic pickup cartridge which is obtained from the embodiment of FIG. 5. In FIG. 6, the yokes 15L and 15R including the pole pieces 16L, 17L, 16R and 17R are injection-molded thereby putting them exactly into place and simplifying their assembly. The yoke-coil unit is housed in the shield case 19 made of an alloy with high magnetic permeability, such as permalloy thereby protecting the unit from the external magnetic fields. The shield case 19 is fixed on the housing 20 with the ends of the coils 18L and 18R connected with the terminals 21 respectively. The parts of the vibration system are mounted on the stylus holder 22 and fitted replaceably in the housing 20, thereby securing them in place with respect to the pole pieces 16L, 17L, 16R and 17R and at the same time facilitating the replacement of the stylus 25. The damper 23 which is interposed between the armature 7 and the support 11 controls the vibration system including the reproducing stylus 25, stylus arm 26 and armature 7. The vibration system is attached to the cartridge from under the yokes 15R and 15L, which makes possible a small and accurate vertical tracking angle, while at the same time minimizing the occurrences of vertical tracking errors. The armature 7 is displaced toward the pole piece 17 by a length corresponding to the static compliance of the supporting portion by the bias force due to the stylus pressure. To prevent this undesired displacement of the armature 7, it is recommended that the shape of the damper 23 should be deformed in the direction of the bias force or such other necessary steps should be taken to correct the dislocation in advance.

Also, the output voltages generated in the coils 18R and 18L wound on the yokes R and 15L are proportional to the vibration velocity of the armature 7 with respect to the pole pieces 16 and 17 or the vibration displacement of the armature 7 under the same frequency. Therefore, in order to obtain a high output, the armature 7 may be enlarged in the direction perpendicular to its thickness, that is to say, the diameter of the armature 7 may be increased. By so doing, the shortcircuited magnetic fluxes as shown by arrow A in FIG. 3a are reduced thereby improving the magnetic efficiency.

The pickup cartridge according to another embodiment of the invention is shown in FIGS. 7a and 7b, which respectively illustrate the construction of its essential parts and a perspective view. In FIG. 7, the pickup is of the monaural type and the yokes 15a and 15b are disposed on both sides of the armature 7 in parallel with the surface of the record disc 24, the coils 18a and 18b being wound on the yokes 15a and 15b respectively. When the reproducing stylus 25 changes its position as shown in FIG. 7a, the magnetic fluxes in the yokes 15a and 15b flow in the directions of arrows E and E respectively and the coils wound on the yokes are connected in series so that output voltages e and e induced in the coils 18a and 18b are added to each other. It is of course possible that the coils 18a and 18b are wound respectively in a pair on the yokes 15a and 15b to cancel external leakage magnetic flux. This arrangement of the yokes 15a and 15b on both sides of the armature permits an output two or four times higher than the preceding embodiments to be produced, and excellent signal to noise ratio.

Still another embodiment of the invention in the form of a stereo pickup cartridge of the 45-45 type is shown in FIGS. 80 and 8b. Referring to FIG. 8a, a pair of yokes 15L are disposed on both sides of the armature 7 along the L axis, and coils 18L which are wound on the yokes are connected in series to produce an output voltage eL. Similarly, a pair of yokes 15R are placed opposite to each other with the armature 7 interposed therebetween on the R axis at right angles to the L axis, and coils 18R which are wound on the yokes 15R are connected in series so that the output voltages eR in both coils are superimposed on each other. As an alternative, each yoke may be wound with a pair of coils for the total number of 8 coils. In the pickup cartridge with this construction, the vibration system comprising the reproducing stylus 25, stylus arm 26 and armature 7 should preferably be inserted into the gap among the oppositely placed yokes 15R and 15L.

It will be understood from the above explanation that the pickup cartridge according to the present invention comprises a permanent armature of a flat plate magnetized such that the same pole is set up on both sides in the direction of thickness while the opposite pole is formed in the central portion thereof and 'a stylus arm with a reproducing stylus attached to its end, wherein the vibration system is so constructed that the main axis of the stylus arm is connected to and pivotally supported in the neighborhood of the center of gravity of the armature in the direction of its magnetic axis so as to vibrate the peripheral portions of the armature in response to the vibration of the reproducing stylus in accordance with the contour of the grooves of the record disc. Also, the two pole pieces at the ends of the inverted channel-shaped yokes of magnetic material are placed in the proximity of the armature, the legs of the yokes being wound each with at least one coil, thereby making up at least one magnetic circuit. According to this arrangement, output voltage is generated by alternation of magnetic fluxes supplied by the inverted channel-shaped yokes in combination with the armature which is magnetized in the transverse direction of the flat plate so as to set up magnetic fields of the same polarity on both sides thereof, resulting not only in a high transducing efficiency but in a high output voltage and reduced distortion thereof. Further, since the stylus arm with the reproducing stylus attached to it is pivot-supported at a fulcrum located at or in the neighborhood of the center of gravity of the armature, both moment of inertia and the effective mass of the vibration system are decreased. This results in a higher limit of frequency range and in a lower mechanical impedance, whereby it is possible to obtain a pickup cartridge of such a superior quality that vibration transmitted from the disc grooves by a low stylus pressure is used for voltage generation. Furthermore, the advantage that two coils may be wound on a single yoke permits external leakage magnetic field to be cancelled, while at the same time increasing an output voltage and reducing noise voltages, resulting in a high signal to noise ratio. In addition, the arrangement of the invention allows the vibration system or stylus assembly to be mounted from under the yoke assembly, which makes possible a smaller vertical tracking angle as well as an appropriate value thereof, minimizing the tracking error in the vertical direction and facilitating the replacement of the reproducing stylus. Finally, the magnetic circuit incorporated in the invention is so simple that the cartridge can be assembled at low cost and with high precision.

What is claimed is:

1. A pickup cartridge comprising an armature comprising a permanent magnet of a flat plate magnetized in the axial direction in the same polarity on both outer sides and in the opposite polarity at the central portion boundary plane, a stylus arm coupled to said armature, a stylus mounted on the end of said stylus arm, a yoke of the substantially inverted channel shape and a coil wound on said yoke, said armature being supported approximately at its center of gravity, said stylus arm being movable in all angular directions, said yoke having a pair of pole pieces disposed in the proximity of said armature.

2. A pickup cartridge according to claim 1, wherein said armature in the form of a flat plate consists of an integral single magnetic material.

3. A pickup cartridge according to claim 1, wherein said armature in the form of a flat plate consists of two flat magnet plates which are bonded with each other 7 and magnetized in the axial direction in such a manner that portions of one polarity of the respective magnet plates are brought into contact with each other.

4. A pickup cartridge according to claim 1, comprisinga pair of substantially inverted-channel shaped yokes disposed in the proximity of the outer periphery of said armature, said yokes being wound with coils connected in series with each other.

5. A pickup cartridge according to claim I, comprising a pair of substantially inverted channel-shaped yokes disposed at right angles to each, other in the proximity of the outer periphery of said armature.

6. A pickup cartridge according to claim 1 in which said armature is provided with a section in the shape of a semicircle,

7. A pickup cartridge according to claim 1, in which said armature is only partially magnetized.

8. A stereophonic pickup cartridge comprising an armature of a flat disc-shaped magnet magnetized in its axial direction and having magnetic poles of the same polarity set up on both outer sides and magnetic poles of the opposite polarity formed in its central portion at the boundary plane, a stylus arm coupled to said armature, a stylus mounted on the end of said stylus arm, a support member with a notch portion for supporting said armature approximately at its center of gravity, a damper of elastic material interposed between said armature and said support member for allowing said stylus arm and said armature to vibrate around said center of gravity, a pair of substantially inverted channelshaped yokes disposed at right angles to each other for effecting stereophonic reproduction from a stereophonic grooved sound record and coils wound on said yokes, said yokes being provided with pole pieces at their ends disposed in the proximity of the outer periphery of said armature.

9. A stereo pickup cartridge according to claim 8, comprising four inverted channel-shaped yokes placed at right angles to each other in the proximity of the outer periphery of said armature, wherein coils wound on each of pairs of said yokes arranged at to each other are connected in series.

10. A pickup cartridge according to claim 8, in which said armature is provided with a section in the shape of a semicircle.

11. A pickup cartridge according to claim 8, in which said armature is provided with a section in the shape of a V.

12. A pickup cartridge according to claim 8, in which said armature is provided with a section in the shape of a 13. A pickup cartridge according to claim 8, wherein said disc-shaped magnet comprises two disc-shaped axially magnetized plates, said plates being bonded to each other at surfaces of like polarity. 

1. A pickup cartridge comprising an armature comprising a permanent magnet of a flat plate magnetized in the axial direction in the same polarity on both outer sides and in the opposite polarity at the central portion boundary plane, a stylus arm coupled to said armature, a stylus mounted on the end of said stylus arm, a yoke of the substantially inverted channel shape and a coil wound on said yoke, said armature being supported approximately at its center of gravity, said stylus arm being movable in all angular directions, said yoke having a pair of pole pieces disposed in the proximity of said armature.
 2. A pickup cartridge according to claim 1, wherein said armature in the form of a flat plate consists of an integral single magnetic material.
 3. A pickup cartridge according to claim 1, wherein said armature in the form of a flat plate consists of two flat magnet plates which are bonded with each other and magnetized in the axial direction in such a manner that portions of one polarity of the respective magnet plates are brought into contact with each other.
 4. A pickup cartridge according to claim 1, comprising a pair of substantially inverted-channel shaped yokes disposed in the proximity of the outer periphery of said armature, said yokes being wound with coils connected in series with each other.
 5. A pickup cartridge according to claim 1, comprising a pair of substantially inverted channel-shaped yokes disposed at right angles to each other in the proximity of the outer periphery of said armature.
 6. A pickup cartridge according to claim 1 in which said armature is provided with a section in the shape of a semicircle,
 7. A pickup cartridge according to claim 1, in which said armature is only partially magnetized.
 8. A stereophonic pickup cartridge comprising an armature of a flat disc-shaped magnet magnetized in its axial direction and having magnetic poles of the same polarity set up on both outer sides and magnetic poles of the opposite polarity formed in its central portion at the boundary plane, a stylus arm coupled to said armature, a stylus mounted on the end of said stylus arm, a support member with a notch portion for supporting said armature approximately at its center of gravity, a damper of elastic material interposed between said armature and said support member for allowing said stylus arm and said armature to vibrate around said center of gravity, a pair of substantially inverted channel-shaped yokes disposed at right angles to each other for effecting stereophonic reproduction from a stereophonic grooved sound record and coils wound on said yokes, said yokes being provided with pole pieces at their ends disposed in the proximity of the outer periphery of said armature.
 9. A stereo pickup cartridge according to claim 8, comprising four inverted channel-shaped yokes placed at right angles to each other in the proximity of the outer periphery of said armature, wherein coils wound on each of pairs of said yokes arranged at 180* to each other are connected in series.
 10. A pickup cartridge according to claim 8, in which said armature is provided with a section in the shape of a semicircle.
 11. A pickuP cartridge according to claim 8, in which said armature is provided with a section in the shape of a V.
 12. A pickup cartridge according to claim 8, in which said armature is provided with a section in the shape of a +.
 13. A pickup cartridge according to claim 8, wherein said disc-shaped magnet comprises two disc-shaped axially magnetized plates, said plates being bonded to each other at surfaces of like polarity. 